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Abstract:

A CD-pitch dependency for a lithographic pattern printing process is
related to the spectral intensity distribution of radiation used for
projecting the pattern. A CD-pitch dependency can vary from one system to
another. This can result in an iso-dense bias mismatch between systems.
The invention addresses this problem by providing a lithographic
apparatus including an illumination system for providing a projection
beam of radiation, a projection system for projecting a patterned beam
onto a target portion of a substrate, and a substrate table for holding
the substrate, with a controller to provide an adjustment of the spectral
distribution of radiant intensity of the projection beam. The adjustment
of the spectral intensity distribution is based on data relating to an
iso dense bias, and comprises a broadening of the spectral bandwidth or a
change of shape of the spectral intensity distribution.

Claims:

1.-20. (canceled)

21. A system comprising: an excimer laser arranged to produce radiation
to expose a radiation-sensitive surface of a substrate in a lithographic
apparatus; and a bandwidth-controller arranged to control a bandwidth of
the spectral distribution of radiant intensity of the radiation, the
bandwidth-controller constructed and arranged to adjust the bandwidth in
reaction to a user supplied signal representative for a selected
bandwidth of the spectral distribution.

22. The system according to claim 21, wherein the user supplied signal is
a signal supplied by the lithographic apparatus.

23. The system according to claim 21, wherein the signal is determined
based on data relating to a feature in a pattern, the pattern being that
of a patterning device used to modulate the radiation for projection onto
a radiation-sensitive target portion of a substrate by a lithographic
apparatus.

24. The system according to claim 23, wherein the data comprises data
relating to a feature arranged at a first pitch and at a second pitch in
a pattern and representing a corresponding first printed size and second
printed size of the feature.

25. The system according to claim 24, wherein the data represent a
difference between the corresponding first printed size and second
printed size of the feature.

26. The system according to claim 21, wherein the adjustment is arranged
to match a parameter of a feature of a pattern as printed on respectively
a first lithographic apparatus and a second lithographic apparatus.

27. The system according to claim 26, wherein the adjustment is arranged
to reduce a difference between a corresponding first printed size and a
second printed size of the feature as printed on respectively the first
lithographic apparatus and the second lithographic apparatus.

28. The system according to claim 21, wherein the spectral distribution
of radiant intensity is a superposition of a first and a second peaked
spectral intensity distribution having a respective first and second
bandwidth, respective first and second peak wavelength, and respective
first and second intensity, and wherein the adjustment comprises a change
of difference between the first and second peak wavelength where the
first and second bandwidth are substantially equal and the first and
second intensity are substantially equal, difference between the first
and second peak wavelength and difference between the first and second
bandwidth, difference between the first and second peak wavelength and
difference between the first and second intensity, or difference between
the first and second peak wavelength and difference between the first and
second bandwidth and difference between the first and second intensity.

29. The system according to claim 28, wherein the difference between the
first and second peak wavelength is greater than 0 and less than or equal
to 1 pm.

30. The system according to claim 21, wherein the spectral distribution
of radiant intensity comprises a spectral intensity peak having, with
respect to a center wavelength, a symmetric shape and wherein the
adjustment comprises a change of the symmetric shape into an asymmetric
shape with respect to the center wavelength.

31. A system comprising: an excimer laser arranged to produce radiation
to expose a radiation-sensitive surface of a substrate in a lithographic
apparatus; and a controller arranged to control the spectral distribution
of radiant intensity of the radiation, the controller constructed and
arranged to adjust the spectral distribution to match a parameter of a
feature of a pattern as printed on respectively a first lithographic
apparatus and a second lithographic apparatus.

32. The system according to claim 31, wherein the feature parameter
comprises a critical dimension and wherein the matching of the parameter
comprises reducing critical dimension variation between the first
lithographic apparatus and the second lithographic apparatus.

33. The system according to claim 31, wherein the feature parameter
comprises a first printed size of the feature arranged at a first pitch
and a second printed size of the feature arranged at a second pitch.

34. The system according to claim 33, wherein feature parameter comprises
a difference between the corresponding first printed size and second
printed size of the feature.

35. The system according to claim 31, wherein the spectral distribution
of radiant intensity is a superposition of a first and a second peaked
spectral intensity distribution having a respective first and second
bandwidth, respective first and second peak wavelength, and respective
first and second intensity, and wherein the adjustment comprises a change
of difference between the first and second peak wavelength where the
first and second bandwidth are substantially equal and the first and
second intensity are substantially equal, difference between the first
and second peak wavelength and difference between the first and second
bandwidth, difference between the first and second peak wavelength and
difference between the first and second intensity, or difference between
the first and second peak wavelength and difference between the first and
second bandwidth and difference between the first and second intensity.

36. A system comprising: a lithographic apparatus configured to project
radiation onto a radiation-sensitive surface of a substrate; and a
controller arranged to control the spectral distribution of radiant
intensity of the radiation, the controller constructed and arranged to
adjust the spectral distribution by supplying a signal representative for
a selected spectral distribution of the radiation to an excimer laser
optically connected to the lithographic apparatus.

37. The system according to claim 36, further comprising the excimer
laser arranged to produce the radiation for the lithographic apparatus.

38. The system according to claim 36, wherein the signal is determined
based on data relating to a feature in a pattern, the pattern being that
of a patterning device used to modulate the radiation for projection onto
the radiation-sensitive surface.

39. The system according to claim 38, wherein the data comprises data
relating to a feature arranged at a first pitch and at a second pitch in
the pattern and representing a corresponding first printed size and
second printed size of the feature.

40. The system according to claim 36, wherein the controller is further
configured to adjust a lithographic apparatus setting in order to vary an
iso-dense bias associated with a pattern of the radiation.

Description:

[0001] The present application is a continuation of co-pending U.S. patent
application Ser. No. 12/838,750, filed on Jul. 19, 2010, now allowed,
which is a continuation of U.S. patent application Ser. No. 11/316,346,
filed on Dec. 23, 2005, now U.S. Pat. No. 7,817,247, which is a
continuation in part of U.S. patent application Ser. No. 11/036,190,
filed Jan. 18, 2005, now abandoned, which is a continuation of U.S.
patent application Ser. No. 11/019,535, filed Dec. 23, 2004, now
abandoned, the entire contents of each foregoing application hereby
incorporated by reference.

FIELD

[0002] The present invention relates to a lithographic apparatus, an
excimer laser and a device manufacturing method. This invention also
relates to a device manufactured thereby.

DESCRIPTION OF THE RELATED ART

[0003] A lithographic apparatus is a machine that applies a desired
pattern onto a target portion of a substrate. Lithographic apparatus can
be used, for example, in the manufacture of integrated circuits (ICs). In
that circumstance, a patterning device, which is alternatively referred
to as a mask or a reticle, may be used to generate a circuit pattern
corresponding to an individual layer of the IC, and this pattern can be
imaged onto a target portion (e.g., comprising one or several dies) on a
substrate (e.g., a silicon wafer) that has a layer of radiation-sensitive
material (resist). In general, a single substrate will contain a network
of adjacent target portions that are successively exposed. Known
lithographic apparatus include so-called steppers, in which each target
portion is irradiated by exposing an entire pattern onto the target
portion at once, and so-called scanners, in which each target portion is
irradiated by scanning the pattern through the projection beam in a given
direction (the "scanning"-direction) while synchronously scanning the
substrate parallel or anti-parallel to this direction.

[0004] Between the reticle and the substrate is disposed a projection
system for imaging the irradiated portion of the reticle onto the target
portion of the substrate. The projection system includes components for
directing, shaping or controlling the projection beam of radiation. The
projection system may, for example, be a refractive optical system, or a
reflective optical system, or a catadioptric optical system, respectively
including refractive optical elements, reflective optical elements, and
both refractive and reflective optical elements.

[0005] Generally, the projection system comprises a device to set the
numerical aperture (commonly referred to as the "NA") of the projection
system. For example, an adjustable NA-diaphragm is provided in a pupil of
the projection system.

[0006] An illumination system may also encompass various types of optical
components, including refractive, reflective, and catadioptric optical
components for directing, shaping, or controlling the projection beam of
radiation, and such components may also be referred to below,
collectively or singularly, as a "lens". The illumination system of the
apparatus typically comprises adjustable optical elements for setting an
outer and/or inner radial extent (commonly referred to as σ-outer
and σ-inner, respectively) of an intensity distribution upstream of
the mask, in a pupil of the illumination system. A specific setting of
σ-outer and σ-inner may be referred to hereinafter as an
annular illumination mode. Controlling the spatial intensity distribution
at a pupil plane of the illumination system can be done to improve the
processing parameters when an image of the illuminated object is
projected onto a substrate.

[0007] Microchip fabrication involves the control of tolerances of a space
or a width between devices and interconnecting lines, or between
features, and/or between elements of a feature such as, for example, two
edges of a feature. In particular the control of space tolerance of the
smallest of such spaces permitted in the fabrication of the device or IC
layer is of importance. Said smallest space and/or smallest width is
referred to as the critical dimension ("CD").

[0008] With conventional projection lithographic techniques it is well
known that an occurrence of a variance in CD for isolated features and
dense features may limit the process latitude (i.e., the available depth
of focus in combination with the allowed amount of residual error in the
dose of exposure of irradiated target portions for a given tolerance on
CD). This problem arises because features on the mask having the same
nominal critical dimensions will print differently depending on their
pitch on the mask (i.e., the separation between adjacent features) due to
pitch dependent diffraction effects. Pitch is the sum of the feature
width and the space between two subsequent features.

[0009] A difference in printed CD between two similar features such as
lines arranged at two respective, different pitches, is referred to as an
iso-dense bias or "IDB". For example, a feature consisting of a line
having a particular line width and arranged at a large pitch, will print
differently from the same feature having the same line width and provided
in a dense arrangement on the mask, i.e., arranged at a small pitch.
Hence, when both dense and isolated features of critical dimension are to
be printed simultaneously, a pitch dependent variation of printed CD is
observed. Data describing a specific CD-pitch dependency are generally
represented by a plot of CD versus pitch, referred to as a CD-pitch curve
hereinafter. The phenomenon "iso-dense bias" is a particular problem in
photolithographic techniques. Iso-dense bias is typically measured in
nanometers and represents an important metric for practical
characterization of lithography processes.

[0010] Generally, a mask pattern is designed in such a way that
differences in dimensions of printed isolated and dense features are
minimized to some degree, by applying a size bias to certain features.
Applying, to the mask pattern, a size bias to certain features such as
lines is referred to as feature-biasing and, in the case of lines, as
line-biasing. The actual pitch dependency of printed CD depends, however,
on the specific properties of the apparatus (such as aberrations and
calibrations of the lithographic apparatus in use). Therefore, even in
the presence of feature bias, a residual iso-dense bias may be present.
Conventional lithographic apparatus do not directly address the problem
of iso-dense bias. Conventionally, it is the responsibility of the users
of conventional lithographic apparatus to attempt to compensate for the
iso-dense bias by either changing the apparatus optical parameters, such
as the NA of the projection lens or the σ-outer and σ-inner
settings, or by designing the mask in such a way that differences in
dimensions of printed isolated and dense features are minimized. However,
such changes of machine settings may adversely affect the process
latitude.

[0011] Generally, in a high volume manufacturing site different
lithographic projection apparatus are to be used for the same
lithographic manufacturing process step to ensure optimal exploitation of
the machines, and consequently (in view of, for example,
machine-to-machine differences) a variance and/or errors in CD may occur
in the manufacturing process. Generally, the actual pitch dependency of
such errors and the actual CD-pitch dependency depends on the specific
layout of the pattern and the features, the aberration of the projection
system of the lithographic apparatus in use, the properties of the
radiation sensitive layer on the substrate, and the radiation beam
properties such as illumination settings, and the exposure dose of
radiation energy. Therefore, given a pattern to be provided by a
patterning device, and to be printed using a specific lithographic
projection apparatus including a specific radiation source, one can
identify data relating to iso-dense bias which are characteristic for
that process, when executed on that lithographic system. In a situation
where different lithographic projection apparatus (of the same type
and/or of different types) are to be used for the same lithographic
manufacturing process step, there is a problem of mutually matching the
corresponding different CD-pitch dependencies, such as to reduce CD
variations occurring in the manufacturing process.

[0012] A known technique to match a CD-pitch dependency of a machine (for
a process whereby an annular illumination mode is used) to a CD-pitch
dependency of another machine is --in analogy with above described
techniques to compensate an iso-dense bias--to change the σ-outer
and σ-inner settings, while maintaining the difference between the
σ-outer and σ-inner settings (i.e., whilst maintaining the
annular ring width of the illumination mode) of one of the two machines.
The nominal σ-settings are chosen so as to optimize the process
latitude (in particular, the depth of focus and the exposure latitude).
Therefore, this approach has the disadvantage that for the machine
whereby the σ-settings are changed, the process latitude is
becoming smaller and may become too small for practical use.

[0013] An actual pitch dependency as described above may be varying in
time. For example, due to lens heating the aberration of the projection
system may vary, and or due to heating and other instabilities properties
such as illumination settings, and exposure dose of radiation energy may
vary in time. Therefore there is the problem of controlling and keeping
within tolerance a desired CD-pitch dependency.

SUMMARY

[0014] The present inventors have identified the following. Techniques are
known to enhance the depth of focus for a projection lithographic process
by manipulating the spectral distribution of radiant intensity of the
projection beam. Generally, radiation used for exposure is provided by an
excimer laser; for example, a KrF excimer laser operating at 248 nm
wavelength or an ArF excimer laser operating at 193 nm wavelength may be
used. The spectral distribution of radiant intensity provided by such
lasers comprises a spectral intensity peak having a symmetric shape with
respect to a peak wavelength λp. The bandwidth of the spectral
peak may be expressed as a full-width half-maximum bandwidth (referred to
as FWHM bandwidth) or alternatively as the bandwidth within which 95% of
the total output power of the laser is contained (referred to as the E95
bandwidth), with the peak wavelength λp typically centered
within said bandwidths.

[0015] The finite magnitude of the bandwidth introduces a "smear out" of
the image of a feature over a focus range around a best focus position
BF. Said smear out is represented by a plurality of images displaced
along the optical axis of the projection system, in accordance with a
plurality of radiation wavelengths (in a range of wavelengths centered at
λp). The plurality of axially displaced images is formed by
the projection system due to the presence of residual axial chromatic
aberration of the projection system. If F is the distance between the
plane of best focus corresponding to the radiation wavelength
λp and an image plane corresponding to the radiation
wavelength λ, the effect of axial chromatic aberration is described
by dF/dλ=AC, where AC is a constant. Therefore, to a good
approximation the effect of a constant defocus of the substrate over a
distance F, during exposure, is the same as the effect of a change of
wavelength Δλ given by Δλ=F/AC and exposing with
radiation of this changed wavelength with the substrate held in the
best-focus focal plane.

[0016] The effects of finite spectral bandwidth of the laser radiation can
be modeled by linearly converting a symmetric laser spectral distribution
of exposure intensity into a symmetric focus distribution using the lens
property AC defined by dF/dλ=AC. Over a fairly wide range of
wavelengths the laser spectrum can be converted linearly into a focus
spectrum using this lens dependency dF/dλ (see FIG. 1a U.S. Patent
Application Publication No. 2002/0048288 A1).

[0017] A finite laser bandwidth results in the re-distribution of the
aerial image through focus. The total aerial image will be a sum of the
aerial images, each aerial image defocused in accordance with F=AC
Δλ, and weighted by the relative exposure intensity at the
wavelength λ=λp+Δλ.

[0018] This addition of (generally defocused) images has an effect on the
image contrast at wafer level. Therefore, laser bandwidth contributes to
the optical proximity effects and the CD-pitch dependency of a system.
The laser bandwidth can vary from system to system. As a result the
proximity behavior and the CD-pitch dependency can differ from system to
system resulting in a proximity-behavior mismatch between different
apparatus or between an actual and a target CD-pitch dependency.

[0019] It is an object of the present invention to obviate or mitigate one
or more of the aforementioned problems in the prior art. In particular,
it is an object of the invention to provide improved control over an
iso-dense bias, both in magnitude as well as over time.

[0020] According to an aspect of the invention there is provided a
lithographic apparatus comprising: [0021] a radiation system for
providing a beam of electro-magnetic radiation having a spectral
distribution of radiant intensity I(λ), a support structure for
supporting a patterning device, the patterning device serving to impart
the beam of radiation with a pattern in its cross-section; [0022] a
substrate table for holding a substrate, a projection system for
projecting the beam of radiation after it has been patterned onto a
target portion of the substrate, and a controller configured and arranged
to provide an adjustment of said spectral distribution of radiant
intensity based on data relating to a feature arranged at a first pitch
and at a second pitch in the pattern and representing a corresponding
first printed size and second printed size of the feature.

[0023] The present invention provides an advantage of adjustment of the
spectral distribution of radiant intensity I(λ): using data
relating to a feature-size with the feature arranged at two different
pitches, such as for example data describing the CD-pitch dependency, it
is possible to match system to system optical proximity behavior.

[0024] According to a further aspect of the invention, there is provided a
device manufacturing method including providing a beam of
electro-magnetic radiation having a spectral distribution of radiant
energy, patterning the beam of radiation with a pattern in its
cross-section using a patterning device, projecting the patterned beam of
radiation onto a target portion of a substrate, and adjusting of said
spectral distribution of radiant intensity in accordance with data
relating to a feature arranged at a first pitch and at a second pitch in
the pattern and representing a corresponding first printed size and
second printed size of the feature.

[0025] Although specific reference may be made in this text to the use of
lithographic apparatus in the manufacture of ICs, it should be understood
that the lithographic apparatus described herein may have other
applications, such as the manufacture of integrated optical systems,
guidance and detection patterns for magnetic domain memories,
liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The
skilled artisan will appreciate that, in the context of such alternative
applications, any use of the terms "wafer" or "die" herein may be
considered as synonymous with the more general terms "substrate" or
"target portion," respectively. The substrate referred to herein may be
processed, before or after exposure, in for example a track (a tool that
typically applies a layer of resist to a substrate and develops the
exposed resist) or a metrology or inspection tool. Where applicable, the
disclosure herein may be applied to such and other substrate processing
tools. Further, the substrate may be processed more than once, for
example in order to create a multi-layer IC, so that the term substrate
used herein may also refer to a substrate that already contains multiple
processed layers.

[0026] The terms "radiation" and "beam" used herein encompass all types of
electromagnetic radiation, including ultraviolet (UV) radiation (e.g.,
having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme
ultra-violet (EUV) radiation (e.g., having a wavelength in the range of
5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0027] The term "patterning device" used herein should be broadly
interpreted as referring to devices that can be used to impart a
projection beam with a pattern in its cross-section such as to create a
pattern in a target portion of the substrate. It should be noted that the
pattern imparted to the projection beam may not exactly correspond to the
desired pattern in the target portion of the substrate. Generally, the
pattern imparted to the projection beam will correspond to a particular
functional layer in a device being created in the target portion, such as
an integrated circuit.

[0028] Patterning devices may be transmissive or reflective. Examples of
patterning devices include masks, programmable mirror arrays, and
programmable LCD panels. Masks are well known in lithography, and include
mask types such as binary, alternating phase-shift, and attenuated
phase-shift, as well as various hybrid mask types. An example of a
programmable mirror array employs a matrix arrangement of small mirrors,
each of which can be individually tilted so as to reflect an incoming
radiation beam in different directions; in this manner, the reflected
beam is patterned. The support structure supports, i.e., bears the weight
of the patterning device. It holds the patterning device in a way
depending on the orientation of the patterning device, the design of the
lithographic apparatus, and other conditions, such as for example whether
or not the patterning device is held in a vacuum environment. The support
can be using mechanical clamping, vacuum, or other clamping techniques,
for example electrostatic clamping under vacuum conditions. The support
structure may be a frame or a table, for example, which may be fixed or
movable as required and which may ensure that the patterning device is at
a desired position, for example with respect to the projection system.
Any use of the terms "reticle" or "mask" herein may be considered
synonymous with the more general term "patterning device."

[0029] The term "projection system" used herein should be broadly
interpreted as encompassing various types of projection system, including
refractive optical systems, reflective optical systems, and catadioptric
optical systems, as appropriate for example for the exposure radiation
being used, or for other factors such as the use of an immersion fluid or
the use of a vacuum. Any use of the term "lens" herein may be considered
as synonymous with the more general term "projection system."

[0030] The lithographic apparatus may be of a type having two (dual stage)
or more substrate tables (and/or two or more mask tables). In such
"multiple stage" machines the additional tables may be used in parallel,
or preparatory steps may be carried out on one or more tables while one
or more other tables are being used for exposure.

[0031] The lithographic apparatus may also be of a type wherein the
substrate is immersed in a liquid having a relatively high refractive
index, e.g., water, so as to fill a space between the final element of
the projection system and the substrate. Immersion techniques are well
known in the art for increasing the numerical aperture of projection
systems.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Embodiments of the invention will now be described, by way of
example only, with reference to the accompanying schematic drawings in
which corresponding reference symbols indicate corresponding parts, and
in which:

[0033] FIG. 1 depicts a lithographic apparatus according to an embodiment
of the invention;

[0034] FIG. 2 depicts a lithographic apparatus according to a further
embodiment of the invention;

[0035] FIG. 3(a) illustrates an example of an asymmetric spectral
intensity distribution with a location of a peak wavelength, a center
wavelength, and E95 wavelengths;

[0038] FIG. 4 illustrates four CD-pitch curves for four different spectral
bandwidths;

[0039] FIG. 5 illustrates a symmetric spectral intensity distribution as a
superposition of two spectrally overlapping intensity distributions and
as a superposition of two mutually displaced spectral intensity
distributions;

[0048] FIG. 14 schematically depicts the effect of a transition from a
relatively narrow, symmetric spectral intensity distribution to a broader
symmetric and to a broader asymmetric spectral intensity distribution on
a Bossung curve for an isolated feature, and

[0049] FIG. 15 depicts a flow diagram illustrating a device manufacturing
method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0050] FIG. 1 schematically depicts a lithographic apparatus according to
a particular embodiment of the invention. The apparatus comprises:
[0051] an illumination system (illuminator) IL for providing a projection
beam PB of radiation (e.g., UV radiation or EUV radiation). [0052] a
first support structure (e.g., a mask table) MT for supporting a
patterning device (e.g., a mask) MA and connected to first positioning
actuator PM for accurately positioning the patterning device with respect
to item PL; [0053] a substrate table (e.g., a wafer table) WT for holding
a substrate (e.g., a resist-coated wafer) W and connected to second
positioning actuator PW for accurately positioning the substrate with
respect to item PL; and [0054] a projection system (e.g., a refractive
projection lens) PL for imaging a pattern imparted to the projection beam
PB by patterning device MA onto a target portion C (e.g., comprising one
or more dies) of the substrate W.

[0055] As here depicted, the apparatus is of a transmissive type (e.g.,
employing a transmissive mask). Alternatively, the apparatus may be of a
reflective type (e.g., employing a programmable mirror array of a type as
referred to above).

[0056] The illuminator IL receives a beam of radiation from a radiation
source SO. The source and the lithographic apparatus may be separate
entities, for example when the source is an excimer laser. In such cases,
the source is not considered to form part of the lithographic apparatus
and the radiation beam is passed from the source SO to the illuminator IL
with the aid of a beam delivery system BD comprising for example suitable
directing mirrors and/or a beam expander. In other cases the source may
be integral part of the apparatus, for example when the source is a
mercury lamp. The source SO and the illuminator IL, together with the
beam delivery system BD if required, may be referred to as a radiation
system.

[0057] The illuminator IL may comprise adjustable optical elements AM for
adjusting the angular intensity distribution of the beam. Generally, at
least the outer and/or inner radial extent (commonly referred to as
σ-outer and σ-inner, respectively) of the intensity
distribution in a pupil plane of the illuminator can be adjusted. In
addition, the illuminator IL generally comprises various other
components, such as an integrator IN and a condenser CO. The illuminator
provides a conditioned beam of radiation, referred to as the projection
beam PB, having a desired uniformity and intensity distribution in its
cross-section.

[0058] The projection beam PB is incident on the mask MA, which is held on
the mask table MT. Having traversed the mask MA, the projection beam PB
passes through the lens PL, which focuses the beam onto a target portion
C of the substrate W. With the aid of the second positioning actuator PW
and position sensor IF (e.g., an interferometric device), the substrate
table WT can be moved accurately, e.g., so as to position different
target portions C in the path of the beam PB. Similarly, the first
positioning actuator PM and another position sensor (which is not
explicitly depicted in FIG. 1) can be used to accurately position the
mask MA with respect to the path of the beam PB, e.g., after mechanical
retrieval from a mask library, or during a scan. In general, movement of
the object tables MT and WT will be realized with the aid of a
long-stroke module (coarse positioning) and a short-stroke module (fine
positioning), which form part of the positioning actuator PM and PW.
However, in the case of a stepper (as opposed to a scanner) the mask
table MT may be connected to a short stroke actuator only, or may be
fixed. Mask MA and substrate W may be aligned using mask alignment marks
M1, M2 and substrate alignment marks P1, P2.

[0059] The depicted apparatus can be used in the following modes, for
example:

[0060] In step mode, the mask table MT and the substrate table WT are kept
essentially stationary, while an entire pattern imparted to the
projection beam is projected onto a target portion C at once(i.e., a
single static exposure). The substrate table WT is then shifted in the X
and/or Y direction so that a different target portion C can be exposed.
In step mode, the maximum size of the exposure field limits the size of
the target portion C imaged in a single static exposure.

[0061] In scan mode, the mask table MT and the substrate table WT are
scanned synchronously while a pattern imparted to the projection beam is
projected onto a target portion C (i.e., a single dynamic exposure). The
velocity and direction of the substrate table WT relative to the mask
table MT is determined by the (de-)magnification and image reversal
characteristics of the projection system PL. In scan mode, the maximum
size of the exposure field limits the width (in the non-scanning
direction) of the target portion in a single dynamic exposure, whereas
the length of the scanning motion determines the height (in the scanning
direction) of the target portion.

[0062] In another mode, the mask table MT is kept essentially stationary
holding a programmable patterning device, and the substrate table WT is
moved or scanned while a pattern imparted to the projection beam is
projected onto a target portion C. In this mode, generally a pulsed
radiation source is employed and the programmable patterning device is
updated as required after each movement of the substrate table WT or in
between successive radiation pulses during a scan. This mode of operation
can be readily applied to maskless lithography that utilizes programmable
patterning devices, such as a programmable mirror array of a type as
referred to above.

[0063] Combinations and/or variations on the above described modes of use
or entirely different modes of use may also be employed.

[0064] FIG. 2 schematically depicts a lithographic apparatus according to
one embodiment of the invention. The apparatus of FIG. 2, in contrast to
the apparatus in FIG. 1, is of a reflective type (e.g., employing a
reflective mask).

[0065] The apparatus of FIG. 2 comprises: [0066] an illumination system
(illuminator) IL configured to condition a radiation beam B (e.g., UV
radiation or EUV radiation); [0067] a support structure (e.g., a mask
table) MT constructed to support a patterning device (e.g., a mask) MA
and connected to a first positioner PM configured to accurately position
the patterning device in accordance with certain parameters; [0068] a
projection system (e.g., a refractive projection lens system) PS
configured to project a pattern imparted to the radiation beam B by
patterning device MA onto a target portion C (e.g., comprising one or
more dies) of the substrate W.

[0069] A difference between the spectral bandwidth of lasers which are
part of respective lithographic projection apparatus result in
differences between a pitch dependent variation of printed CD for these
respective apparatus. Thus, a difference between the respective CD-pitch
dependencies may occur. The present invention seeks to address this
problem by providing an apparatus which is equipped with a controller
configured and arranged to provide an adjustment of the spectral
distribution of the laser radiation whereby the adjustment is aimed at
affecting the CD-pitch dependency of the lithographic apparatus. The
adjustment may be a dynamic adjustment to compensate for variations in
time of an iso-dense bias. Such variations in time may, for example, be
caused by lens heating due to absorption of laser beam radiation during
exposure. The CD-pitch dependency is specific for the apparatus in
combination with the layout of the mask pattern and other process
parameters and properties such as for example the illumination mode and
setting, the exposure time, the resist type, the specific lens
aberrations, as well as settings for the pre-exposure and post exposure
processing steps.

[0070] As explained above, a CD-pitch dependency can be affected,
according to the present invention, by adjusting the spectral intensity
distribution of the laser beam. An excimer laser generally is provided
with means to control and adjust the spectral distribution of the emitted
laser radiation. For example U.S. Patent Application Publication No.
2002/0048288A1 relates to an excimer laser provided with a controller of
a line-narrowing device for controlling a the spectral distribution of
the laser beam. The controller is arranged to adjust the bandwidth of the
spectral distribution by dithering a wavelength tuning mirror in phase
with the repetition rate of the laser. The line narrowing unit comprises
a grating and a fast tuning mechanism, and the controller controls a
monitoring of the laser beam to determine bandwidth of individual pulses
laser pulses, and a periodically adjusting of the tuning mechanism during
a series of pulses so that the wavelengths of some pulses in the series
of pulses are slightly longer than a target wavelength and the
wavelengths of some pulses in the series of pulses are slightly shorter
than the target wavelength in order to produce for the series of pulses
an effective laser beam spectrum having at least two spectral peaks. In
the latter case, the spectral distribution of radiant intensity may for
example be a superposition of a first and a second peaked spectral
intensity distribution having a respective equal first and second
full-width half-maximum bandwidth, and a respective equal first and
second intensity. The spectral peaks feature a respective first and
second peak wavelength, and the difference Δλp between
the first and second peak wavelength is adjustable.

[0071] Similarly, U.S. Pat. No. 5,303,002 relates to an excimer laser
which generates a beam of radiation whereby the spectral distribution of
radiant intensity of the laser beam of radiation comprises a plurality of
narrow spectral bands of radiation. A line narrowing device is arranged
to select one or more line narrowed outputs to be used for the
lithographic process. Each of the outputs may have an attenuator which
can adjust the intensity of each spectral band independently. The
corresponding radiation beams pass through a gain generator and are
combined to produce a beam of radiation with the desired spectral
distribution.

[0072] The modified spectral intensity distribution may be an asymmetric
distribution, i.e. a distribution with a spectral shape deviating from a
symmetric shape with respect to a center wavelength λc.

[0073] Referring to FIG. 3(a), there is shown an example of an asymmetric
spectral distribution 300. The wavelengths λ1 and
λ2 in FIG. 3(a) define the E95 bandwidth represented by the
arrow 301. The wavelength λc is the center wave length, i.e.
the wavelength at the center of the range [λ1, λ2].
The curve 300 represents the spectral intensity distribution I(λ),
which is peaked at a peak wavelength λp. In general, an
asymmetric intensity distribution is characterized by the inequality
I(λ-λc)≠I(λc-λ) . A measure for
asymmetry may be expressed in terms of the moments of intensity
MIleft and MIright defined as

[0074] and the spectrum may be referred to as asymmetric when MIleft
is different from MIright. For example, the spectrum may be referred
to as asymmetric when the spectral intensity distribution I(λ) is
an asymmetric distribution whereby the moments of intensity, as defined
in equation (1), satisfy the inequality

[0077] FIG. 4 illustrates several CD-pitch curves obtained by simulation
of a lithographic process. Each of the simulated CD-against-pitch curves
relates to a line feature occurring at different pitches. The line width
to be printed is 150 nm; the corresponding pitch of a 1:1 duty cycle
dense pattern of these lines is 300 nm. The spectral distribution of
laser radiation is symmetric, and the CD-pitch curves 402, 403, and 404
are parameterized by the E95 bandwidth of the spectral peak. The plot 401
represents the iso-dens bias characteristic for the ideal case whereby
the laser radiation is monochromatic. The CD-pitch curves 402, 403, and
404 represent the CD versus pitch behaviour of the lithographic process
for respectively an E95 bandwidth of 0.52 pm, 0.8 pm, and 1.2 pm. Whereas
at 300 nm pitch a variation of laser bandwidth has practically no effect,
the printed line width (CD) for lines arranged at, for example 800 nm
pitch is dependent on the laser bandwidth.

[0078] According to the present invention, the line biasing at the mask
may for example be chosen such as to compensate the variations of IDB
characteristic 403. Lines at a pitch of 300 nm are line-biased with 17 nm
and lines arranged at 800 nm are line-biased 35 nm, in order to obtain
equal printed line width of 150 nm (printed CD) for both pitches.

[0079] However, since line width variations can be caused by a multitude
of errors such as focus and dose variations, exposure tool imperfections
such as c value variations, projection lens aberrations, or flare, a
residual iso-dense bias error may occur in spite of using above described
feature biased mask pattern for exposure. This residual iso-dense bias
may either be predicted using apparatus data and a computer-simulation of
the lithographic process, or, alternatively, may be measured by running a
calibration measurement. In both ways, data relating to the line-feature
arranged at a first pitch (for example, 300 nm) and at a second pitch
(for example, 800 nm) in the pattern and representing the corresponding
first printed line width and second printed line width of the
line-feature can be obtained.

[0080] A deviation at 300 nm pitch of the printed line width may, for
example, be compensated by adjusting the exposure dose. The data obtained
may be corrected for this exposure dose adjustment. As a result, the
expected printed CD at 800 nm pitch may then be 1.5 or 2 nanometer too
small (when, for example, the apparatus and process in use is
characterized by plot 404). From the behaviour of CD as a function of
laser spectral bandwidth at 800 nm pitch, an adjustment of the spectral
distribution of radiant intensity based on the data (and corrected for
exposure dose adjustment in this example) may be applied in accordance
with the characteristics 404 and 403: a decrease of the bandwidth by 0.3
pm will lead to an increase of line width at 800 nm pitch by 1.5 to 2 nm,
without affecting the line width at 300 nm pitch.

[0081] Alternatively, the expected printed line width at 800 nm pitch may
be 2 nanometer too big (for example, the apparatus and process in use is
characterized by plot 302), in which case an adjustment of the spectral
distribution of radiant intensity based on the data (and corrected for
exposure dose adjustment) may be applied in accordance with the
characteristics 402 and 403: an increase of the bandwidth by 0.4 pm will
lead to a decrease of line width at 800 nm pitch by about 2 nm, again
without substantially affecting the line width at 300 nm pitch. According
to the present invention, an adjustment of the laser spectral intensity
distribution can be used as described above to provide an adjustment of a
CD-pitch dependency. Such an adjustment can be used to reduce optical
proximity effects or residual optical proximity effects in a lithographic
printing process, or to reduce differences between different CD-pitch
dependencies of different apparatus.

[0082] According to an aspect of the invention, the adjustment described
above is obtained using an excimer laser whereby the spectral
distribution of radiant intensity is a superposition of two equal but
spectrally displaced, peaked spectral intensity distributions having an
equal first and second full-width half-maximum bandwidth, and a
respective equal first and second intensity, and whereby the difference
Δλp between the first and second peak wavelength is
adjustable in a range from 0 to 0.5 pm and more particularly from 0 to 1
pm. With these ranges, and with typical axial chromatic aberration
(absolute) values for the coefficient AC, such as for example in a range
from 150 nm/pm to 400 nm/pm, smear out of the image covers a range of
about -400 to +400 nm around best focus which is a practical range for
adjusting or matching an iso-dense bias.

[0083] According to an aspect of the invention the source SO in FIG. 1 is
an excimer laser providing a pulsed beam of laser radiation. The laser
comprises bandwidth monitoring equipment and wavelength tuning equipment
permitting bandwidth control of the laser beam by a bandwidth-controller
of the laser. The bandwidth-controller of the laser is generally used to
maintain a preselected bandwidth (compensating, for example, changes in
the laser-gain medium over the life of the laser), in accordance with a
selection made by the laser manufacturer. According to the present
invention, however, the bandwidth-controller of the laser is provided
with an input channel arranged for receiving a signal representative for
a selected bandwidth of the spectral distribution in accordance with a
selection made by the user of the laser. For example, the signal can be
provided by the controller of the lithographic apparatus according to the
present invention. With an eximer laser featuring a user-selectable
spectral bandwidth the adjustment of iso-dense bias according to the
present invention can be provided dynamically, for example, during a
scanning exposure of a target portion C or during a plurality of
exposures of target portions C covering a substrate. Both intra-die and
inter die controll of iso-dense bias is obtained this way. Similarly, an
eximer laser provided with user-selectable spectral bandwidth setting can
be used to obtain iso-dense bias matching between different apparatus, in
accordance with the present invention.

[0084] FIG. 5 illustrates a spectral distribution of radiant intensity 500
as a superposition of a first peaked spectral intensity distribution 501
and a second peaked spectral intensity distribution 502 having a
respective equal first bandwidth 503 and second bandwidth 504. The
respective first and second peak intensities as well as the first and
second peak wavelengths λp1 and λp2 are equal. FIG.
5 further illustrates the effect of providing, through control of the
line width narrowing device of the pulsed excimer laser, an adjustment
comprising a change Δλp of the difference between the
first and second peak wavelength. The adjustment is (the difference
λp1-λp2 in FIG. 5 being initially zero) in the
present example equal to the difference λp2-λp1.
The resulting intensity distribution 506 has a bandwidth 507 larger than
the initial bandwidth 505.

[0085] Referring to FIG. 6 there is shown a schematic representation of a
Bossung curve 600 typical for an isolated feature and a Bossung curve 601
typical for the feature in dense arrangement, i.e., arranged at a duty
cycle 1:1. The Bossung curve 600 represents a plot of printed critical
dimension for the feature in isolated arrangement, and the corresponding
CD is denoted by CDiso, as it would be obtained with exposure in
different focal positions. The exposure energy is a constant along the
plots 600 and 601. The different focal positions are given by the focal
coordinate F (above referred to as a "defocus"), which defines the
position of the substrate with respect to a position of best focus BF.

[0086] Typically, the printed critical dimension CDdense of the dense
feature does not depend (to a first approximation) on focal position,
because of the extended depth of focus resulting from two beam imaging.
Generally, imaging of dense features is arranged such that only two
diffracted orders of radiation, as emerging from the pattern, are
captured by the imaging projection lens.

[0087] The printed critical dimension CDiso may be modelled as a
polynomial of F according to

CDiso=A0+A1F+A2F2+A4F4, (2)

[0088] whereby the coefficient A0 represents the printed CD at best
focus. Further, the coordinate F may be expressed in terms of an absolute
focus coordinate f defined by

[0089] F=f-fBF, where the coordinate fBF is the absolute
coordinate, along the z-axis, of the best focus position BF.

[0090] In the absence of a so-called linear focus term, i.e. when
A1=0, the resulting second order approximation denoted by CDiso
(0,2; f) of CDiso is then given by

CDiso(0,2;f)=A0+A2(f-fBF)2. (3)

[0091] In contrast, the Bossung curve for the dense feature may simply be
modeled as CDdense=B0. Thus, at best focus BF, the dense
features are printed at a width B0, and the isolated features at a
width A0, and the iso-dense bias between thee features would be
A0-B0 nm.

[0092] In accordance with the present invention, the effects of finite
spectral bandwidth on the Bossung curve can be modeled by linearly
converting a symmetric spectral intensity distribution of the laser beam
into a symmetric focus distribution using the lens property AC defined by
dF/dλ=AC. Since F=f-fBF, also df/dλ=AC at or near best
focus position. The laser bandwidth results in the re-distribution of the
aerial image through focus. The total aerial image will be a sum of the
aerial images, each aerial image defocused in accordance with F=AC
Δλ, and weighted by the relative exposure intensity at each
wavelength λ. The weighting may be expressed by a weight-function W
in accordance with the spectral distribution of radiant intensity
I(λ) of the laser radiation.

[0093] The resulting printed CD incorporating the effect of the addition
of the (generally defocused) images may be represented by CDav, and
can be approximated by the following averaging:

[0095] For simplicity it will be assumed that the weight function W(f) in
accordance with the symmetric intensity distribution 302 of FIG. 3 can be
approached by a block function 700, as illustrated in FIG. 7.

[0096] Combination of this approximation with the approximation CDiso
(0,2; f) for the printed CD of an isolated feature, results in the
following prediction for the average CD (at best focus) of a feature due
to the introduction of a finite laser bandwidth (resulting in the
re-distribution of the aerial image over a focus range of from
-1/2FBW to 1/2FBW):

[0097] From the above equation it is clear that the change
ΔCDiso in printed critical dimension at best focus (due to a
change from ideal monochromatic radiation to the introduction of a
certain laser bandwidth resulting in a through focus re-distribution of
the image over a focus range from -1/2FBWto 1/2FBW) is given by

Δ CD iso = A 2 1 12 F BW 2 ˜ F BW
2 ##EQU00005##

[0098] In contrast, no such change occurs for the size of the dense
features, since in the present approximation CDdense is a constant
value, independent of focus position: CDdense=B0, in accordance
with the iso-dense characteristics as illustrated in FIG. 4.

[0099] FIG. 8 schematically illustrates the effect of the change from an
ideal practically monochromatic radiation spectrum of the laser beam to
the introduction of a finite laser bandwidth in accordance with the
present approximation. The arrow 800 represents the (focus independent)
shift ΔCDiso of the Bossung curve 600 representing the printed
CD as obtained with the exposure process using a practically
monochromatic (not bandwidth broadened) laser radiation spectrum, and the
curve 810 is the Bossung curve for the increased laser bandwidth. Since
generally the Bossung curve for the feature in dense arrangement is less
or not sensitive to a change of spectral bandwidth, the adjustment of
spectral bandwidth can be used for adjusting the CD-pitch dependency.

[0100] Assuming that the energy dependence of the CD is focus independent
an undesired residual impact of laser bandwidth on printed CD could be
easily compensated in order to maintain the CD of a reference feature
(such as for example the dense lines in the present embodiment)
unaltered.

[0101] The same approximation as described above can be generalized for an
arbitrary defocus position F (and using F=f-fBF) as follows:

[0106] So the re-distribution of the aerial image over a focus range from
-1/2FBW to 1/2FBW does not impact the linear focus term.

[0107] According to an embodiment of the invention, the spectral
distribution of radiant intensity comprises a spectral intensity peak
having, with respect to a center wavelength, a symmetric shape and
wherein said adjustment comprises a change of the symmetric shape into an
asymmetric shape with respect to the center wavelength.

[0108] An asymmetric spectral distribution of radiant intensity of the
laser beam can be provided, for example, by differently attenuating each
of a plurality of narrow spectral bands of radiation in a line narrowing
device which is arranged to select a plurality of line narrowed outputs
to be used for the lithographic process. In FIG. 9 a asymmetric intensity
distribution I(λ) is represented by the plot 300. Similar to the
embodiment described above, the intensity distribution may be
approximated by adjacent, block shaped intensity distributions. In
particular, as is illustrated in FIG. 9, in the present embodiment the
intensity distribution is modelled as two adjacent block functions 910
and 920, of equal area, and different width. The E95 wavelengths
λ1 and λ2 define a total bandwidth equivalent to
the focus range 901 with a magnitude denoted by 3/2FBW, and the
spectrum is approximated by the left block function 910 of width
1/2FBW and the right block function 920 of bandwidth FBW. As
described above for a symmetric intensity distribution, the present
asymmetric spectral radiant intensity distribution may be converted into
a weight function W(f) proportional to the spectral distribution of
radiant intensity I(λ) by expressing I(λ), or in this
embodiment by expressing the block functions representing I(λ)) as
a function of (λ-λc), and writing λ-λc
as an equivalent focal coordinate f with (λ-λc)=f/AC, in
view of the lens property df/dλ=AC. Since the block functions 910
and 920 are of equal area, the exposure dose in the corresponding focus
ranges is equal.

[0109] The effect of a change of the spectral intensity distribution which
initially is representing a quasi monochromatic laser line into an
asymmetric spectral intensity distribution on a Bossung curve can be
estimated using the procedure as described above.

[0110] A combination of the present approximation for the intensity
distribution I(λ) (resulting in to adjacent block-shaped weight
functions) with the approximation CDiso (0,2; f) for the printed CD
of an isolated feature, results in the following prediction for the
average critical dimension CDav (at arbitrary defocus F):

[0111] As schematically indicated in FIG. 10, not only an offset 900 with
magnitude

1 4 A 2 F Bw 2 ##EQU00010## [0112] is introduced (similar to
the situation whereby an increase of bandwidth of a symmetric spectral
distribution is applied) but also a linear term

[0112] 1 2 A 2 FF BW ##EQU00011## [0113] is introduced. The
presence of these two contributions results in a shifted and tilted
Bossung curve (910), as schematically indicated in FIG. 10. Further, the
focus position along the optical axis where a change of critical
dimension as a function of a change of focal position is zero, is now
located at a defocus position Fiso slightly defocused from the best
focus position fBF.

[0114] Since the Bossung curve for the feature in dense arrangement again
is not changing (in the present approximation), a transition from a
narrow symmetric intensity distribution to an asymmetric intensity
distribution could be used to adjust a CD-pitch dependency.

[0115] The impact of varying the asymmetry of a spectral intensity
distribution I(λ) is shown by way of simulations and illustrated in
FIG. 11 and FIG. 12. FIG. 11 shows different asymmetric spectral
intensity distributions 111, 112, 113, and 114. For the simulations these
spectral intensity distributions were approximated. FIG. 12 shows the
simulated effect of increased spectral asymmetry for constant FWHM (Full
Width Half Maximum=0.2 pm), and for nominal 65 nm dense and isolated
lines (Prolith 5 pass calculation, NA 0.93 and sigma 0.94/0.74, binary
reticle, calibrated resist model). The Bossung curves 111', 112', 113',
and 114' correspond to the respective spectra 111, 112, 113, and 114. As
expected from the calculations, the effect is a shift of the Bossung
curve along the focus-axis and change of the tilt of the Bossung curve at
a fixed focus. Note that all calculations were performed using the same
exposure dose. Further, FIG. 12 shows that the Bossung curve 115 for
dense lines is not affected by the spectral adjustment. Therefore, the
adjustment can successfully be used for adjusting a CD-pitch dependency.

[0116] FIG. 13 shows simulated effect of increased asymmetry of the laser
spectral intensity distribution for constant FWHM=0.2 pm, as shown in
FIG. 11, on an iso-dense bias value for nominal 65 nm dense and isolated
lines. Showing the impact on iso dense bias when correcting for the focus
offset introduced by the asymmetry of the spectral distribution. The
magnitude of the impact is application dependent (feature size and shape,
resist and illumination conditions/mode).

[0117] Referring to FIG. 14, examples of Bossung curves 140, 141, 142 show
the impact of a transition from a conventional relatively narrow and
symmetrical spectral intensity distribution (143) to a symmetrical
bandwidth-broadened distribution (144) and to an asymmetrical spectral
intensity distribution (145). The dashed lines indicate the approximation
used for the weight function W(f). The Bossung curve for dense lines is
not shown, and is unaffected, thereby providing two independent
parameters for adjusting an iso dense bias characteristic of an
apparatus. Note for both the symmetrical and asymmetrical case the total
focal range 146 is the same.

[0118] According to an aspect of the present invention a device
manufacturing method may exploit the possibility to adjust an iso dense
characteristic by adjustment of the spectral intensity distribution of
the projection beam radiation, as provided by, for example, an excimer
laser, in order to keep the CD-pitch dependency within tolerance or to
maintain a matching of the CD-pitch dependency to a target CD-pitch
dependency. As illustrated in FIG. 15, a first step 150 of the method
comprises obtaining iso-dense bias data the apparatus and the process run
on the apparatus, i.e., data relating to a feature arranged at a first
pitch and at a second pitch in the pattern and representing a
corresponding first printed size and second printed size of the feature.
Next, comparing these data with target data, step 151 in FIG. 15, yields
information on the desired change of the iso-dense bias. Next, a first
adjustment of the iso-dense bias is provided by adjusting a lithographic
apparatus setting (such as for example an exposure dose, a sigma setting,
and a setting of illumination mode parameters) such that for one pitch
the features will be printed at the desired critical dimension. This
first adjustment is depicted by step 152. An independent second
adjustment of the iso-dense bias is next obtained by adjusting the
spectral intensity distribution of the projection beam radiation, step
153. The latter step can be exploited to establish the printing of the
desired critical dimension for features arranged at the second pitch.
Before printing the pattern (step 154), if the obtained, adjusted
iso-dense bias is not yet satisfactory, the steps 152 and 153 can be
repeated until the adjusted iso-dense bias is sufficiently close to the
target iso-dense bias.

[0119] According to an embodiment, there is provided a lithographic
apparatus comprising: a radiation system for providing a beam of
electro-magnetic radiation having a spectral distribution of radiant
intensity; a support structure for supporting a patterning device, the
patterning device serving to impart the beam of radiation with a pattern
in its cross-section; a substrate table for holding a substrate; a
projection system for projecting the beam of radiation after it has been
patterned onto a target portion of the substrate; and a controller
configured and arranged to provide an adjustment of said spectral
distribution of radiant intensity based on data relating to a feature
arranged at a first pitch and at a second pitch in the pattern and
representing a corresponding first printed size and second printed size
of the feature.

[0120] In an embodiment, the spectral distribution of radiant intensity
comprises a spectral intensity peak having a bandwidth and wherein said
adjustment comprises a change of the bandwidth. In an embodiment, the
spectral distribution of radiant intensity is a superposition of a first
and a second peaked spectral intensity distribution having a respective
equal first and second bandwidth, and a respective equal first and second
intensity, and a respective first and second peak wavelength, and wherein
the adjustment comprises a change of difference between the first and
second peak wavelength. In an embodiment, the spectral distribution of
radiant intensity comprises a spectral intensity peak having, with
respect to a center wavelength, a symmetric shape and wherein said
adjustment comprises a change of the symmetric shape into an asymmetric
shape with respect to the center wavelength. In an embodiment, the data
represent a difference between the corresponding first printed size and
second printed size of the feature. In an embodiment, the data further
comprise a target difference between the corresponding first printed size
and second printed size of the feature. In an embodiment, the adjustment
of said spectral distribution of radiant intensity is arranged to match
the difference to the target difference. In an embodiment, the target
difference is a difference between the corresponding first printed size
and second printed size of the feature, as printed using the patterning
device on a supplementary lithographic apparatus. In an embodiment, the
radiation controller controls a source of the beam of radiation. In an
embodiment, the spectral distribution of radiant intensity is a
superposition of a first and a second peaked spectral intensity
distribution having a respective first and second bandwidth, first and
second peak wavelength, and first and second intensity, and wherein said
adjustment comprises a change of one of difference between the first and
second peak wavelength and difference between the first and second
bandwidth, difference between the first and second peak wavelength and
difference between the first and second intensity, or difference between
the first and second peak wavelength and difference between the first and
second bandwidth and difference between the first and second intensity.
In an embodiment, the difference between the first and second peak
wavelength is selected from the group consisting of between 0 and 1 pm,
and between 0 and 0.5 pm. In an embodiment, the radiation system
comprises an excimer laser to provide the beam of radiation and having a
bandwidth-controller arranged to control a bandwidth of the spectral
distribution of radiant intensity, and whereby the bandwidth-controller
is constructed and arranged to adjust the bandwidth in reaction to a user
supplied signal representative for a selected bandwidth of the spectral
distribution. In an embodiment, the signal representative for a selected
bandwidth of the spectral distribution is provided by the controller.

[0121] In an embodiment, there is provided an excimer laser having a
bandwidth-controller arranged to control a bandwidth of the spectral
distribution of radiant intensity, and whereby the bandwidth-controller
is constructed and arranged to adjust the bandwidth in reaction to a user
supplied signal representative for a selected bandwidth of the spectral
distribution.

[0122] In an embodiment, there is provided a device manufacturing method
comprising: providing a beam of electro-magnetic radiation having a
spectral distribution of radiant intensity; patterning the beam of
radiation with a pattern in its cross-section using a patterning device;
projecting the patterned beam of radiation onto a target portion of a
substrate; and adjusting of said spectral distribution of radiant
intensity in accordance with data relating to a feature arranged at a
first pitch and at a second pitch in the pattern and representing a
corresponding first printed size and second printed size of the feature.

[0123] In an embodiment, the spectral distribution of radiant intensity
comprises a spectral intensity peak having a bandwidth and wherein said
adjusting comprises changing the bandwidth. In an embodiment, the
spectral distribution of radiant intensity comprises a spectral intensity
peak shaped symmetrically with respect to a center wavelength and wherein
said adjusting comprises changing the spectral intensity peak into a
spectral intensity peak shaped asymmetrically with respect to the center
wavelength. In an embodiment, the data represent a difference between the
corresponding first printed size and second printed size of the feature.
In an embodiment, the data further comprise a target difference between
the corresponding first printed size and second printed size of the
feature. In an embodiment, the adjusting of said spectral distribution of
radiant intensity comprises matching the difference to the target
difference. In an embodiment, the target difference is a difference
between the corresponding first printed size and second printed size of
the feature, as printed using the patterning device on respectively a
first lithographic apparatus and a second lithographic apparatus. In an
embodiment, the adjusting is provided during one of a scanning exposure
of a target portion on a substrate and a plurality of scanning exposures
of a corresponding plurality of target portions on a substrate.

[0124] In an embodiment, there is provided a microelectronic device
manufactured according to a method described above.

[0125] While specific embodiments of the invention have been described
above, it will be appreciated that the invention may be practiced
otherwise than as described. The description is not intended to limit the
invention. It will also be appreciated that the disclosed embodiments may
include any of the features herein claimed.